Chemistry Structure 2: Models of Bonding and Structure

What are cations?

Positive ions formed after METAL atoms LOSE electrons

How do you name a cation?

Name of element + “ion”

What are anions?

Negative ions formed after NONMETAL ions GAIN electrons

How do you name an anion?

Element name + -ide + “ion”

How does hydrogen behave with a metal vs a nonmetal?

Hydrogens are cations when bonded to nonmetal, but anions when bonded to metals.

How do you find the ion that an element forms?

1. Determine if it is a metal or a nonmetal to find out if it will form a cation or anion

2. Write out the element’s e-configuration

3. Subtract (for cations) and add (for anions) to completely empty or fill the element’s valence shell

4. Name the ion according its element and the amount of electrons added/subtracted

What type of ions do Transition metals form?

Cations

How do you name an ionic compound involving a Transition metal?

1. Identify the charge of the anion

2. Cross the charges of the anion and the transition metal

3. Use Roman numerals to indicate the charge of the transition metal that is required to make the bond neutral

4. Name the ionic compound using the name of the transition metal + anion + -ide

What is an ionic bond?

The electrostatic attraction between two oppositely charged ions

Which types of elements form ionic bonds?

Metals + Nonmetals

What are the physical characteristics of ionic compounds? (5)

1. Hard, crystalline structure

2. Soluble in a liquid state or in an aqueous solution in POLAR solvents

3. High electrical conductivity as liquids/aqueous solutions

4. Low volatility

5. High Melting Point

Why do ionic compounds have a high melting point and low volatility?

It requires more energy to break through their ionic bonds because they are polar, so it is harder to volatize or melt ionic compounds

What does the strength of an ionic bond depend on?

The charge of the ion and the radius of the metal ion - the higher the charge and smaller the radius, the stronger the bond

What is a covalent bond?

The electrostatic attraction between a shared pair of electrons and their positively charged nuclei

Which type of element forms covalent bonds?

Nonmetals + Nonmetals

What are the steps to drawing a Lewis structure?

1. Count the total # of valence electrons

2. Identify the central atom

3. Draw surrounding atoms with one single bond to the central atom

4. Add electrons according to the octet rule

5. Count the total # of electrons so that it matches the # from step 1

6. If there are too many electrons, start forming double/triple bonds and repeat steps 4 and 5

What are the physical characteristics of covalent compounds? (5)

1. Softer, more flexible structure

2. May be soluble in water but stay as molecules when dissolved rather than breaking apart into ions

3. Are poor conductors

4. Volatile

5. Low Melting Point

Why do covalent compounds have low melting points and higher volatility?

It requires less energy to break through covalent bonds because they are relatively weak, so it is easier to volatize or melt covalent compounds

What are coordination bonds?

A type of covalent bond where both of the shared electrons come from the same atom

What are Resonance Structures?

Sets of lewis structures that are various forms of the same compound

What is bond order?

The number of chemical bonds between a pair of atoms indicating the stability of their bonds.

When a compound has multiple resonance structures, the bond order is an average of the different bond orders of each resonance structure.

What is the respective bond order, strength, and length of single, double, and triple bonds (not involved in resonance)

Single Bonds: 1, weak, long

Double Bonds: 2, stronger, medium

Triple Bonds: 3, strongest, short

What is bond polarity?

The differences in electronegativity between bonded atoms, which leads to the formation of dipoles

How do you calculate % ionic character?

Difference in Electronegativity / 3.2

What are the respective ranges of electronegativity difference values for non-polar covalent bonds, polar covalent bonds, and ionic bonds?

Non-polar/weakly polar covalent bonds: 0.0-0.5

Polar covalent bonds: 0.5-1.7

Ionic bonds: 1.8+

What is molecular polarity?

What are Giant Covalent Structures?

A large network of atoms joined by covalent bonds

Why do Giant Covalent Structures not have intermolecular forces?

They are considered as one molecule, with only intramolecular covalent bonds holding each atom together

What are the physical characteristics of Giant Covalent Structures? (5)

1. Very hard, solid structures

2. Are insoluble in all solvents (polar and non-polar)

3. Are poor conductors (except graphite)

4. Low volatility

5. Very High Melting Points

Why do Giant Covalent structures have very high melting points, low volatility, and low solubility?

It requires more energy to break through their covalent bonds because there are so many of them, making it harder to volatize or melt Giant Covalent structures

What are allotropes?

Different forms of an element in the same state

What are common allotropes of Carbon? (5)

Graphite, Diamond, Fullerene, Graphene, Buckminsterfullerene

What are common allotropes of Silicon? (2)

Amorphous Silicon and Crystalline Silicon

What are intermolecular forces?

Forces between molecules that determine their physical properties

What are the Van der Waals Forces?

London Dispersion Forces and Dipole-Dipole Attractions

What is Hydrogen Bonding?

A special type of dipole-dipole attraction that occurs only between H and O/N/F

What are London Dispersion Forces and which types of molecules do they occur in?

Forces caused by the constant movement of electrons within an atom/molecule that occur in ALL molecules

What are Dipole-Dipole Forces and which types of molecules do they occur in?

Forces caused by the electrostatic attraction between the partially positive and partially negative parts of different molecules

What is the difference between the types of dipoles involved in LDFs and Dipole-Dipole forces?

LDFs involve INSTANTENEOUS and INDUCED dipoles while Dipole-Dipole forces involve PERMANENT dipoles

What is the relationship between LDFs and molar mass?

LDFs increase as a molecule’s molar mass increases, which also increases its boiling point

Which type of intermolecular force causes water to have a high boiling point?

Hydrogen bonding

List the intermolecular forces in order from strongest to weakest

Hydrogen Bonding, Dipole-Dipole forces, London Dispersion Forces

What is a metallic bond?

The electrostatic attraction between a lattice of metal cations and delocalized electrons

What are the physical characteristics of metallic compounds? (5)

1. Structures are relatively hard, some may be softer but most are relatively malleable

2. Are insoluble in water

3. Conductive as solids

4. Low volatility

5. Relatively High Melting Points

Why are metallic compounds malleable and thermally conductive?

Delocalized electrons cause non-directional bonding, which allows layers within the cation lattice to slide past each other into different shapes when put under stress.

Free-moving delocalized electrons allow better better flow for heat and electricity, making metals more conductive.

What does the strength of a metallic bond depend on?

The charge of the ion and the radius of the metal ion - the higher the charge and smaller the radius, the stronger the bond

What are alloys?

Mixtures of different metals that have enhanced properties (ex. stronger, less corrosive)

Alloys are often less malleable because the different sizes of atoms make it harder for delocalized electrons to move.

List in order from highest to lowest melting point:

Giant Covalent Structures, Metals, Polar Covalent Compounds, Non-polar Covalent Compounds, Ionic Compounds

Giant Covalent Structures, Ionic Compounds, Metals, Polar Covalent Compounds, Non-Polar Covalent Compounds

What three tests would you perform to test if a substance is an ionic compound?

1. Test if it conducts electricity as a liquid, but not as a solid

2. Test if it is soluble in a polar solvent

3. Test if it has a high melting point